Most/many people with MECFS respond positively to steroids—we’ve already discussed this and you said you weren’t sure about the mechanism.
I have been trying to think of something useful to add to the debate here. I am not sure I know enough answers though. Prednisolone has often been used as a way of testing to see if an illness is inflammatory - as judged by an immediate response. However, it also produces a high for a lot of people regardless of inflammation.
The other point is that symptoms in ME may be due to signals that often go with inflammation but are not actually part of inflammation per se. As an example, injection of a bacterial extract like typhoid vaccine will produce the malaise that usually goes with inflammation without there being any actual inflammation. The toxins have a direct effect on the hypothalamus without any tissues actually being inflamed.
The fact that a number of people with ME seem to get relief from steroids does suggest to me that these sorts of signals are involved but it may not be true for all. Nevertheless, in the long term steroids tend to have more risks than benefits and very often the beneficial effect wears off.